The 300 boxes of documents were unearthed after four elderly Kenyans took steps earlier this year to sue the Foreign and Commonwealth Office (FCO), claiming they were tortured between 1952 and 1960.

A judge ordered the Foreign Office to produce all relevant evidence.

The 1500 files held by the National Archives allegedly include details of the detention and punishment of suspected rebels in the country.

The files were removed from Kenya in 1963, and secretly brought to Britain days before a declaration of independence was declared in the African nation. It was thought the files had been destroyed but were found after a trawl through archives.

The four claimants, who arrived in Britain on Monday, are seeking “damages for personal injuries caused by repeated assaults perpetrated by employees and agents of the British Colonial Administration in Kenya when they were detained”.

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Their lawyers will likely claim the evidence indicates that assaults were “part of a system of torture, inhumane and degrading treatment applied by police, Home Guards and other members of the security services with the knowledge of the Colonial Administration”.

The Kenyans are seeking a “statement of regret” from the Government and a welfare fund for victims. It is thought about 1,400 other former Mau Mau detainees remain alive today.

President Barack Obama's grandfather, Hussein Onyango Obama, was detained in the 1950s Mau Mau uprising against British colonial rule.

The FCO told The Times it was not legally liable in the case, which starts on Thursday.